ivan_kholodov

/[а-яА-ЯёЁ\s\.\,\!\?\-]/gm // - кирилица. Забыл в первой версии ответа большую Ё

function max(data, key = n => n) {
  const getVal = key instanceof Function ? key : n => n[key];
  let result = null;

  for (const n of data) {
    const val = getVal(n);
    result = (!result || result[1] < val) ? [ n, val ] : result;
  }

  return result?.[0];
}

const { text } = max(arr, n => n.text.length);
const oldest = max(arr, 'age');

const result = arr.flat().map((n, i) => ({ ...n, id: -~i }));

const result = [];

for (const n of arr) {
  for (const m of n) {
    result.push({
      ...m,
      id: result.length + 1,
    });
  }
}